S. C. Fang

The absorption of radioactive 2,4-dichlorophenoxyacetic acid and the translocation of C14 by bean plants☆☆☆

Abstract A small amount of radioactivity was found in different parts of bean plants as early as 2 hr. after treatment with radioactive 2,4-dichloro-phenoxyacetic acid (2,4-D), indicating that it is quickly absorbed and the C 14 translocated. Only a small amount of C 14 is translocated to the untreated leaf, root, and terminal bud. The stem (first internode and hypocotyl) is the area where the greatest amount of radioactivity accumulates and increases with time. Young plants will absorb 2,4-D and translocate C 14 more quickly than will the older plants. The absorption of 2,4-D and translocation of C 14 is not dependent on the amount applied above 50 μg. when applied to a single leaf. A small amount of 2,4-D was found to be broken down and metabolized in the bean plant with consequent loss of radioactive CO 2 .

Microbiological assay method for thiamine using Lactobacillus fermenti 36 as test organism.

Summary (1) Maltose or takadiastase digested starch has been found to be one of the many growth stimulants for L. fermenti 36 in assay of thiamine. It is also stimulatory to L. arabinosus 17-5 and Strep, jaecalis R. in assays of pantothenic acid and pyridoxine. (2) Evidence has been obtained to prove that a precaution should be made on thiamine assay of starchy substances using L. fermenti 36 as test organism. Addition of enzyme digested starch or maltose to the assay medium is recommended.

Thiamine Sparing Action of Ascorbic Acid on Lactobacillus Fermenti 36.

Summary 1. Ascorbic acid has been found to have thiamine sparing action on the growth of L. jermenti 36. The addition of both ascorbic acid and thiamine gives a greater growth response than either one when added alone. 2. Addition of pyrithiamine inhibits the utilization of ascorbic acid for growth of L. jermenti 36 in a thiamine-free medium. This result shows that ascorbic acid may function in part by stimulating the synthesis of thiamine. 3. Addition of iodoacetate, 2,4-dinitrophenol or sodium fluoride to the thiamine assay medium containing either thiamine or ascorbic acid shows the difference in inhibition of growth of L. jermenti 36. These results indicate that ascorbic acid must also function in a different metabolic pathway as compared to thiamine in carbohydrate metabolism. 4. It was found that L. jermenti 36 was able to synthesize thiamine when ascorbic acid was present. With the presence of both ascorbic acid and thiamine in the assay medium, the cell was found to contain more thiamine than the cell grown in thiamine medium alone.